GB2245206A

GB2245206A - Brazing procedure in an inert atmosphere

Info

Publication number: GB2245206A
Application number: GB9110859A
Authority: GB
Inventors: Chikara Fujiwara; Takashi Onda; Akira Fukushima
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1990-05-30
Filing date: 1991-05-21
Publication date: 1992-01-02
Anticipated expiration: 2011-05-21
Also published as: GB2245206B; GB9110859D0; US5188281A; JPH0433794A

Abstract

A brazing procedure, comprising the steps of retaining a component having a brazing section therein by means of a die which is compressed by a hot press, admitting an inert gas into the component to achieve an inert atmosphere inside the component having a pressure which is higher than the external pressure, and then heating the component for thereby brazing the section to be brazed. <IMAGE>

Description

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DESCRIPTION BRAZING PROCEDURE IN AN INERT ATMOSPHERE

The present invention relates to a brazing procedure in an inert atmosphere for application to hollow fan blades such as those used in aviation and general industrial gas turbines.

Hollow fan blades for gas turbines have traditionally been manufactured in accordance with a vacuum brazing method using a vacuum furnace.

The prior art vacuum brazing method has suffered from the problems encountered in brazing components having large and complicated configurations as explained hereinafter.

(1) When the components to be brazed have threedimensional curved brazing surfaces, it is difficult to hold the brazed surface accurately in position, thereby rendering it difficult to control the brazing clearance and causing a defective brazing performance.

(2) A change in the configuration might likely occur due to the selfweight of the component to be brazed.

(3) A long brazing cycle is required.

(4) Inconsistent heating is caused to occur when brazing large-sized components.

(5) The brazing equipment is expensive in terms of cost.

j In accordance with a first aspect of the present invention, there is provided a brazing procedure comprising the steps of retaining a component. on the inside of which there is a brazing section to be brazed, by means of a die which is compressed by a hot press, admitting an inert gas into the component to achieve an inert atmosphere inside the component having a pressure which is higher than the external pressure, and then heating the component for thereby brazing said brazing section.

In accordance with a second aspect of the present invention, there is provided a brazing procedure comprising the steps of sealing the circumference of the component having a brazing section to be brazed therein, retaining the component in position by means of a die which is compressed by a hot press, admitting an inert gas into the component to achieve an inert atmosphere inside the component having a pressure which is higher than the external pressure, and then heating the component for thereby brazing said brazing section.

In the above-described procedure, sealing may be achieved around the component having the brazing section therein. This component is compressed and held in place by means of the die which is compressed by the hot press, allowing an operator to precisely -3control the brazing clearance for a brazing section having a complicated configuration.

Subsequently. the inert gas is admitted into the component interior, and the pressure in the interior of the component is raised so as to be higher than the external pressure. Thus. the outer surface of the component may retain the configuration of the surface of the die utilising the differential pressure therebetween to prevent its deformation under its self-weight. With the component heated by means of the hot press, an inert atmosphere prevails in the interior of the component and a satisfactory brazing operation is ensured.

Futhermore. since the clearance may be controlled to a precise level, a satisfactory brazing may be achieved. Moreover, since the interior of the component is maintained at a pressure which is higher than the external pressure utilising an inert gas, and the outer surface of the component is urged against the surface of the die, the configuration of the outer surface of the component can consequently be maintained precisely. The use of the hot press can achieve a low-cost brazing operation.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is a diagrammatic view illustrating a first embodiment of the present invention; and Fig. 2 is a view showing in detail the section II in Fig. 1.

Referring to the drawings, an Ar gas admission tube 6 is welded to a skin 1 made from Ti-6 Al-4V. A brazing material (Ti-20Cu-20Ni-20Zr) is then coated over the dimple head 2a of the dimple core made from Ti-6A1-4V by low pressure plasma spraying. Then. two sheets of the above skins 1 and the dimple core 2 are laminated together in position, and then welded therearound to form a seal using the inert gas (TIG) welding technique, whereby to form a component 7. The component 7, comprising the skin 1 and the dimple core 2 which have been laminated and sealed, is set up beforehand in position between dies 3 and 4 which have been preheated to a temperature of 650 C, and the internal air is exhausted under vacuum through the tube 6 provided on the skin 1. The dies 3 and 4, and the component 7 are heated up by means of asideheater 5, and the skin 1 and the dimple core 2 are subject to a hot-sizing operation, while further continuing this vacuum exhaustion. At this time, the brazing clearance is controlled to be less than the spraying film thickness (about 50 p m).

When the above mentioned dies 3 and 4, and the 1 -5component 7 are heated up to a temperature of 750 C, the vacuum exhausting operation is discontinued and Ar gas is introduced into the interior of the component 7, its pressure being retained at a level which is higher than the external pressure on the component. for example. 5 Torr above atmospheric pressure or around 765 Torr. The above heating operation is continued until the brazing temperature of 900 is reached, and then this brazing temperature is maintained for 10 minutes. Then. the component is caused to be cooled down, and, when the temperature has dropped to 6500 C, the component is withdrawn from the press 8, thus completing the brazing operation.

In the procedure of the present invention, since the component 7 around which a seal welding is created is compressed together by the dies 3 and 4 which pinch the component therebetween by means of a press 8. it is possible to precisely control the brazing clearance of a brazing section having a complicated configuration (three-dimensional curved surface). After the vacuum exhausting operation of the above component 7 is completed and while the component is heated up, an inert gas is admitted so as to flow into the interior of the component. Thus, the brazing section may be maintained in an inert atmosphere, and therefore the brazing operation can also be done in an -6atmospheric furnace (hot press). Furthermore, since -the inert gas pressure at the brazing section is present at a level which is slightly higher than the atmospheric pressure, the outer surface of the brazing component 7 may retain its configuration conforming with those of the dies 3 and 4 due to the differential pressure created between the inside and the outside. whereby to prevent the deformation of the brazing component 7 under its self-weight. Moreover, since the above dies 3 and 4 are heated up beforehand to an approximate temperature of 600 C, the time needed to complete one brazing cycle can be substantially shortened compared to that in the vacuum brazing operation. The hot press which may be used to carry out the above brazing operation represents an improvement over the prior vacuum furnace for its consistent and uniform heating effect for large-sized components and for its reduced cost in the brazing operation.

In the above described procedure for the inert atmosphere brazing operation. the component having a brazing section therein is retained in position by means of a die which is in turn compressed by the hot press. The component is heated up, while its internal portion is pressurised by an inert gas which has been admitted into the component to carry out the brazing 9 -7operation. Since the brazing section may be controlled with precision, a satisfactory brazing operation results. Moreover. since the inert gas is utilised to keep the pressure in the interior of the component at a level higher than the external pressure, and the component is forced at its outer surface against the surface of the die. the outer configuration of the component may therefore be maintained with an enhanced precision. Futhermore. the use of the hot press may reduce the cost of performing the brazing operation.

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Claims

-8CLAIMS

1. A brazing procedure, comprising the steps of retaining a component, on the inside of which there is a brazing section to be brazed. by means of a die which is compressed by a hot press, admitting an inert gas into the component to achieve an inert atmosphere inside the component having a pressure which is higher than the external pressure. and then heating the component for thereby brazing said brazing section.

2. A brazing procedure, comprising the steps of sealing the circumference of the component having a brazing section to be brazed therein, retaining thecomponent in position by means of a die which is compressed by a hot press, admitting an inert gas into the component to achieve an inert atmosphere inside the component having a pressure which is higher than the external pressure, and then heating the component for thereby brazing said brazing section.

3. A brazing procedure, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

Published 1991 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 I RH. Further copies may be obtained from Sales Branch, Unit 6. Nine Mile Point. Cwmfelinfach, Cross Keys. Newport. NP1 7HZ. Printed by Multiplex techniques ltd. St Mary Cray, Kent.

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